1. Field of the Invention
The present invention relates generally to fasteners, and in particular to an encapsulated fastener and a method and tooling for manufacturing same.
2. Description of the Related Art
Mechanical fasteners are available in a wide variety of designs, which accommodate various objects being joined. The specific fastener design features are generally determined by such criteria as the functional requirements of the applications, the static and dynamic loads imposed thereon, the materials being fastened and the operating environment.
Threaded fasteners include bolts, nuts, screws, threaded rods and the like. An advantage of such fasteners is that they can be tightened and loosened with readily available hand and power tools. Consequently, threaded fasteners are used extensively in construction, manufacturing and other industries.
Although steel is a logical material choice for many fasteners based on high strength and low cost, many steel alloys are susceptible to rust, corrosion and galvanic action. Such effects can be countered in some applications by making the fasteners of stainless steel and other alloys that are resistant to rust and corrosion. However, such materials tend to be relatively expensive or ineffective in applications requiring the cost-effectiveness and material strength of steel. Another solution is to zinc-coat (i.e. galvanize), paint or otherwise provide surface protection for the fasteners. However, such solutions can be ineffective in highly corrosive liquid environments, such as salt water, wastewater, process chemicals, acid compounds and base compounds. Examples of highly corrosive dry materials include fertilizers, calcium chloride and other caustic powders and granular materials. In addition to corrosion resistance, impact and abrasion resistance are important design objectives for fasteners installed in severe service applications.
Fasteners that can withstand such severe service conditions are used extensively in the construction of tanks and other vessels for processing, storing and transporting highly corrosive liquids and solid bulk materials. Various applications for such fasteners are found in a number of industries, including petrochemical, manufacturing, agriculture, transportation, construction, defense, etc.
For example, large tanks and storage vessels are commonly constructed on site using prefabricated steel panels, which can be coated or lined with suitable corrosion-resistant materials. Bolting the panels together on site tends to be a relatively efficient and cost-effective construction method. Moreover, bolts and nuts have the advantage of installing with basic hand and power tools.
The prior art includes bolts and nuts encapsulated in injection-molded plastics, which can provide the necessary chemical resistance and other physical characteristics for these applications. For example, snap-on and spin-on plastic covers have previously been utilized for protecting the exposed portions of nut-and-bolt fasteners. The prior art also includes deep metal nuts with blind-end threaded receivers with sufficient lengths to enclose the bolts. Such nuts can be coated with anti-corrosive materials. However, such specialized fasteners tend to be more expensive than standard-size nuts. Moreover, manufacturing techniques generally require gripping the extended nuts by their interior internal threads in order for the entire exterior surface to be effectively coated. Another prior art nut encapsulation technique involves encapsulating standard size nuts in plastic materials with extensions adapted for receiving the bolt shafts protruding from the nuts. Problems with such encapsulation configurations include misalignment between bolt and extension internal threads and unsupported extensions when the extension bores are oversized to avoid contact with the bolt shafts received therein.
Heretofore there have not been available an encapsulated fastener and a method and tooling for manufacturing same with the advantages and features of the present invention.